1. Field of the Invention
This invention relates to two-component, film-forming reactive systems for the surface-to-surface bonding and/or coating of substrates, more particularly for heat-sealable coatings, based on aqueous dispersions of
at least one epoxy-curable resin (I) and
epoxy compounds as curing agent (II)
and to their use. The invention also relates to a process for the production of composites and adhesive-coated substrates.
2. Discussion of Related Art
The production of laminates and composites and especially the production of base materials for flexible printed circuits requires special adhesive systems. The requirements which such systems have to meet are very stringent because on the one hand materials difficult to bond, such as for example copper foils to polyimide films, have to be bonded and because, on the other hand, the composite materials obtained have to be flexible and highly resistant to heat. Solvent-containing adhesive systems based on modified polyurethane, polyester, acrylate and epoxy resins are known to the expert for such purposes. Besides the basic problems of solvents, systems of this type are often attended by the disadvantage that the cure times are far too long, for example up to 14 days in the case of polyurethane adhesive systems, or the curing temperatures are too high, for example up to 240.degree. C. in the case of epoxy resin or acrylate systems. To eliminate the problems posed by solvents, water-based systems have been developed. Thus, water-based adhesives for flexible printed circuits containing dispersions of acrylate (co)polymers and epoxy compounds are known from JP 87/153371 and from JP 85/118781. A major disadvantage of systems such as these are the relatively long cure times, for example 16 hours at 130.degree. C. in the case of JP 87/153371. JP 87/112676 describes water-containing polyurethane adhesives based on polyurethane dispersions (A) obtained from polytetramethylene glycol (MW 400 to 2,000), an organic diisocyanate and a dimethylol carboxylic acid and also hydrazine or dihydrazides as chain extenders neutralized with tertiary amines and a water-soluble compound (B) containing two or more epoxy or aziridine rings per molecule. Although it is stated by way of example that various films, for example PET and polypropylene, can be bonded to one another with this adhesive, there is nothing in the document in question to suggest to the expert that adhesives of the type in question could be suitable for heat-sealable coatings. In addition, there are no references to the production of non-blocking coatings or to the use of the adhesives for the production of flexible printed circuits.
The problem addressed by the present invention was to provide water-based reactive systems which would be capable of developing high bond strengths, even on substrates which are difficult to bond, such as polyimides. In addition, high flexibility, high insulation resistance, high heat resistance and good solder bath resistance would all be guaranteed. The cure time would be relatively short while the curing temperature would be below 200.degree. C. In addition, the particular requirement of blocking resistance would be satisfied. By this is meant the non-tackiness of a film at typical ambient temperatures and storage temperatures which is obtained by coating a substrate with the reactive system according to the invention and subsequent drying. In addition, a new raw material base and a different class of polymers would be opened up as starting material for systems of the type in question.